Bug #21655: segfault when building 3.3.10, regression from 3.3.9

• Status: Open
• Assignee: -
• Target version: -
• ruby -v: ruby 3.3.10 (2025-10-23 revision 343ea05002) [x86_64-linux]
• Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN

[kurly (Greg Kubaryk)]

ref downstream bug https://bugs.gentoo.org/965095 - reporting upstream because I was able to reproduce the problem from ruby-3.3.10.tar.xz manually

build log excerpt; the rest will be provided as an attachment

gcc -O2 -pipe -march=amdfam10  -L. -fstack-protector-strong -rdynamic -Wl,-export-dynamic -fstack-protector-strong -pie  main.o dmydln.o miniinit.o dmyext.o array.o ast.o bignum.o class.o compar.o compile.o complex.o cont.o debug.o debug_counter.o dir.o dln_find.o encoding.o enum.o enumerator.o error.o eval.o file.o gc.o hash.o inits.o io.o io_buffer.o iseq.o load.o marshal.o math.o memory_view.o rjit.o rjit_c.o node.o node_dump.o numeric.o object.o pack.o parse.o parser_st.o proc.o process.o ractor.o random.o range.o rational.o re.o regcomp.o regenc.o regerror.o regexec.o regparse.o regsyntax.o ruby.o ruby_parser.o scheduler.o shape.o signal.o sprintf.o st.o strftime.o string.o struct.o symbol.o thread.o time.o transcode.o util.o variable.o version.o vm.o vm_backtrace.o vm_dump.o vm_sync.o vm_trace.o weakmap.o prism/api_node.o prism/api_pack.o prism/diagnostic.o prism/encoding.o prism/extension.o prism/node.o prism/options.o prism/pack.o prism/prettyprint.o prism/regexp.o prism/serialize.o prism/token_type.o prism/util/pm_buffer.o prism/util/pm_char.o prism/util/pm_constant_pool.o prism/util/pm_list.o prism/util/pm_memchr.o prism/util/pm_newline_list.o prism/util/pm_state_stack.o prism/util/pm_string.o prism/util/pm_string_list.o prism/util/pm_strncasecmp.o prism/util/pm_strpbrk.o prism/prism.o prism_init.o yjit.o yjit/target/release/libyjit.o coroutine/amd64/Context.o  enc/ascii.o enc/us_ascii.o enc/unicode.o enc/utf_8.o enc/trans/newline.o setproctitle.o addr2line.o  -lz -lrt -lrt -lgmp -ldl -lcrypt -lm -lpthread  -o miniruby
:
./miniruby -I./lib -I. -I.ext/common  ./tool/generic_erb.rb -o builtin_binary.inc \
	./template/builtin_binary.inc.tmpl
make: *** [uncommon.mk:1316: builtin_binary.inc] Segmentation fault (core dumped)

[kurly (Greg Kubaryk)]

backtrace using a gentoo-built build with -ggdb3 added to CFLAGS

beans ~ # cd /var/tmp/portage/dev-lang/ruby-3.3.10/work/ruby-3.3.10/
beans /var/tmp/portage/dev-lang/ruby-3.3.10/work/ruby-3.3.10 # gdb --args ./miniruby -I./lib -I. -I.ext/common  -n -e 'BEGIN{version=ARGV.shift;mis=ARGV.dup}' -e 'END{abort "UNICODE version mismatch: #{mis}" unless mis.empty?}' -e '(mis.delete(ARGF.path); ARGF.close) if /ONIG_UNICODE_VERSION_STRING +"#{Regexp.quote(version)}"/o' 15.0.0 ./enc/unicode/15.0.0/casefold.h ./enc/unicode/15.0.0/name2ctype.h ./miniruby -I./lib -I. -I.ext/common  ./tool/generic_erb.rb -o builtin_binary.inc ./template/builtin_binary.inc.tmpl
GNU gdb (Gentoo 16.3 vanilla) 16.3
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Reading symbols from ./miniruby...
warning: File "/var/tmp/portage/dev-lang/ruby-3.3.10/work/ruby-3.3.10/.gdbinit" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load".
To enable execution of this file add
	add-auto-load-safe-path /var/tmp/portage/dev-lang/ruby-3.3.10/work/ruby-3.3.10/.gdbinit
line to your configuration file "/root/.config/gdb/gdbinit".
To completely disable this security protection add
	set auto-load safe-path /
line to your configuration file "/root/.config/gdb/gdbinit".
For more information about this security protection see the
"Auto-loading safe path" section in the GDB manual.  E.g., run from the shell:
	info "(gdb)Auto-loading safe path"
(gdb) run
Starting program: /var/tmp/portage/dev-lang/ruby-3.3.10/work/ruby-3.3.10/miniruby -I./lib -I. -I.ext/common -n -e BEGIN\{version=ARGV.shift\;mis=ARGV.dup\} -e END\{abort\ \"UNICODE\ version\ mismatch:\ \#\{mis\}\"\ unless\ mis.empty\?\} -e \(mis.delete\(ARGF.path\)\;\ ARGF.close\)\ if\ /ONIG_UNICODE_VERSION_STRING\ +\"\#\{Regexp.quote\(version\)\}\"/o 15.0.0 ./enc/unicode/15.0.0/casefold.h ./enc/unicode/15.0.0/name2ctype.h ./miniruby -I./lib -I. -I.ext/common ./tool/generic_erb.rb -o builtin_binary.inc ./template/builtin_binary.inc.tmpl
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7c76d69 in malloc_usable_size () from /lib64/libc.so.6
(gdb) bt
#0  0x00007ffff7c76d69 in malloc_usable_size () from /lib64/libc.so.6
#1  0x000055555563b490 in objspace_malloc_size (objspace=0x5555559a7550, ptr=0x45005555559e6dc0, hint=<optimized out>)
    at gc.c:12381
#2  objspace_xrealloc (objspace=0x5555559a7550, ptr=0x45005555559e6dc0, new_size=18, old_size=<optimized out>) at gc.c:12689
#3  0x0000555555760a8a in rb_str_resize (str=str@entry=140737348585000, len=17) at string.c:3179
#4  0x0000555555760c2d in rb_fstring (str=str@entry=140737348585000) at ./include/ruby/internal/core/rstring.h:369
#5  0x00005555557a32c8 in build_const_pathname (head=<optimized out>, tail=140737348585040) at variable.c:397
#6  rb_set_class_path_string (klass=klass@entry=140737348547760, under=under@entry=140737348551920, name=140737348585040)
    at variable.c:417
#7  0x000055555559c2f4 in rb_define_class_id_under_no_pin (outer=140737348551920, id=10891, super=140737348552240, 
    super@entry=93824992527378) at class.c:1035
#8  0x000055555559c412 in rb_define_class_id_under (outer=<optimized out>, id=<optimized out>, super=super@entry=93824992527378)
    at class.c:1045
#9  0x000055555559c470 in rb_define_class_under (outer=<optimized out>, name=name@entry=0x555555846fdc "EADDRINUSE", 
    super=93824992527378) at class.c:1006
#10 0x000055555560e153 in set_syserr (n=n@entry=98, name=name@entry=0x555555846fdc "EADDRINUSE") at error.c:2711
#11 0x00005555556148e9 in Init_syserr () at /var/tmp/portage/dev-lang/ruby-3.3.10/work/ruby-3.3.10/known_errors.inc:18
#12 0x0000555555647eaa in rb_call_inits () at inits.c:40
#13 0x0000555555618943 in ruby_setup () at eval.c:89
#14 0x000055555561a40d in ruby_init () at eval.c:101
#15 0x0000555555576193 in rb_main (argc=22, argv=0x7fffffffe098) at ./main.c:38
#16 main (argc=<optimized out>, argv=<optimized out>) at ./main.c:64
(gdb) frame 3
#3  0x0000555555760a8a in rb_str_resize (str=str@entry=140737348585000, len=17) at string.c:3179
3179	            SIZED_REALLOC_N(RSTRING(str)->as.heap.ptr, char,
(gdb) p str
$1 = 140737348585000
(gdb) p *str
$2 = 8396805
(gdb) 

[hsbt (Hiroshi SHIBATA)]

• Description updated (diff)

[kurly (Greg Kubaryk)]

Thank you for fixing the markdown in the comment 0.

On an affected machine, I was able to bisect the git repo between tags v3_3_9 and v3_3_10:

5a8d7642168f4ea0d9331fded3033c225bbc36c5 is the first bad commit
commit 5a8d7642168f4ea0d9331fded3033c225bbc36c5 (HEAD)
Author:     nagachika <[e-mail]>
AuthorDate: Wed Oct 8 22:55:33 2025 +0900
Commit:     nagachika <[e-mail]>
CommitDate: Wed Oct 8 22:56:02 2025 +0900

    merge revision(s) 43dbb9a93f4de3f1170d7d18641c30e81cc08365, 2bb6fe3854e2a4854bb89bfce4eaaea9d848fd1b, 7c9dd0ecff61153b96473c6c51d5582e809da489: [Backport #21629]
    
            [PATCH] [Bug #21629] Enable `nonstring` attribute on clang 21
    
            [PATCH] [Bug #21629] Initialize `struct RString`
    
            [PATCH] [Bug #21629] Initialize `struct RArray`

 error.c                                | 2 +-
 ext/-test-/string/fstring.c            | 2 +-
 include/ruby/internal/attr/nonstring.h | 8 ++++++++
 include/ruby/internal/core/rbasic.h    | 3 +++
 include/ruby/internal/core/rstring.h   | 2 +-
 load.c                                 | 4 ++--
 marshal.c                              | 2 +-
 string.c                               | 8 ++++----
 symbol.c                               | 8 ++++----
 version.h                              | 2 +-
 10 files changed, 26 insertions(+), 15 deletions(-)

I was not able to reproduce the build failure for ruby 3.3.10 on an Ubuntu 24.04 machine using gcc-13.3.0.

[kurly (Greg Kubaryk)]

I manually bisected inside that "bad" commit and found that this minimal diff on top of v3_3_10 eliminates the build failure:

diff --git a/include/ruby/internal/core/rstring.h b/include/ruby/internal/core/rstring.h
index 9cf9daa97c..0bca74e688 100644
--- a/include/ruby/internal/core/rstring.h
+++ b/include/ruby/internal/core/rstring.h
@@ -395,7 +395,7 @@ rbimpl_rstring_getmem(VALUE str)
     }
     else {
         /* Expecting compilers to optimize this on-stack struct away. */
-        struct RString retval = {RBASIC_INIT};
+        struct RString retval;
         retval.len = RSTRING_LEN(str);
         retval.as.heap.ptr = RSTRING(str)->as.embed.ary;
         return retval;

[alanwu (Alan Wu)]

It's surprising that leaving the temporary struct uninitialized avoids the crash. Smells like a GCC bug or some UB on our end the optimizer is exploiting.

Does ./configure optflags=-fno-strict-aliasing ... help?

[kurly (Greg Kubaryk)]

alanwu (Alan Wu) wrote in #note-5:

It's surprising that leaving the temporary struct uninitialized avoids the crash. Smells like a GCC bug or some UB on our end the optimizer is exploiting.

Does ./configure optflags=-fno-strict-aliasing ... help?

It doesn't appear to, when added to CFLAGS nor optflags.

[kurly (Greg Kubaryk)]

alanwu (Alan Wu) wrote in #note-5:

It's surprising that leaving the temporary struct uninitialized avoids the crash. Smells like a GCC bug or some UB on our end the optimizer is exploiting.

Does ./configure optflags=-fno-strict-aliasing ... help?

Per a suggestion on the downstream bug, I tried adding -fno-ipa-modref to CFLAGS, and that was sufficient to fix the build.

[alanwu (Alan Wu)]

Looks like you're not building with LTO, so the miscomp from ipa-modref should be in rb_str_resize(). That should be enough for a bug report for GCC, since they need a preprocessed C file.

Maybe this is hitting the same GCC bug as this: https://patchwork.sourceware.org/project/gdb/patch/[e-mail]/#206552 which -fno-ipa-modref also fixes. Unfortunately the bug on GCC side is still unresolved: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120987

[thesamesam (Sam James)]

alanwu (Alan Wu) wrote in #note-8:

Looks like you're not building with LTO, so the miscomp from ipa-modref should be in rb_str_resize(). That should be enough for a bug report for GCC, since they need a preprocessed C file.

Maybe this is hitting the same GCC bug as this: https://patchwork.sourceware.org/project/gdb/patch/[e-mail]/#206552 which -fno-ipa-modref also fixes. Unfortunately the bug on GCC side is still unresolved: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120987

That bug has a patch which should workaround (or fix, it's not clear) that specific issue, but I asked OP to test that and it didn't help this bug. But it may (or may not) still be an issue in modref, just probably not that bug.

[thesamesam (Sam James)]

Reminds me a bit of https://bugs.ruby-lang.org/issues/21516 as well.